My friend was telling me that 1970 W30 Q-jets did not use primary metering rods. Is this true? If so could someone please explain how these could run at part throttle very well? Did they just use larger jets? Why did Olds choose not to use primary rods (if this is true?). Thank you.

 

1970 W30 & W31 4 speed cars did not use a primary piston or rods. 7040256 & 7040255 respectively, they used jets common to the 2 bbl carb, .057 or .058 iirc. Automatic cars used piston & rods w/ normal(.069 & bigger) jets & rods.

 

Actually they used SMALLER jets since there wasn't a metering rod stuck in the middle of them. The power piston was removed because with the low vacuum of the 328 degree cam, the piston would have been in the up position all the time anyway.

 

Ok - thank you! So the vacuum holds the piston down correct? With low vacuum the piston would be up all the time - correct? So they used smaller main jets because there were no rods - was this ok for part throttle?

Reason Im asking is that Im wondering what would happen if someone were to do this to a regular Qjet if they had a really radical cam. Is this what the Qjet rebuilders do when they setup a carb for a really wild combo? Were these carbs just as responsive as the regular Qjet , and were these only used on the 4spd cars?

You guys are great. Im so glad I found this site!!!

 

You have to define responsive as the W-30 and W31's I would consider somewhat lazy in the lower rpm's. I had a W-31 for 35 years and below 3500 it was a little lazy but from 3500 to 6500 hold on to your shorts......They were that way because of the BIG (long duration) cams that were installed...It idled, Kinda, at 8 inches of vacuum.....If you want to modify a regular quadrajet you will need to plug power piston port or you will have a huge vacume leak

Some of us would install 58 jets for the 57 and then grind about an 1/8 of an inch off the top of the accelerator pump to add more fuel on acceleration.....

and then would use a "long tip" (AX) secondary metering rod.

 

Back in the day of my youth and ignorance I took my W-30 4-spd to the local "expert" carb shop. I was told upon pick up of my freshly rebuilt carb that "somebody sure 'Mickey Moused' that carburetor of yours". After that the car just never ran as hard as it did it before it was rebuilt. I'm guessing that he was not familiar with how the W carb was set up and rebuilt it to regular Quadrajet specs. Would this be a fair assumption? And where can I find the exact specs for how this carb should be rebuilt?

It's been a looong time since I've driven this car but I remember before the rebuild there was a heavy bog at full throttle mash. But as soon as she caught her breath !!!!. After the rebuild, the bog wasn't as bad but the following acceleration; while still impressive, was shall we say not quite as......exhilarating.

 

Your bog may be as simple as the secondary air valve adjustmnent. Are you knowledgeable about the Quadrajet?.... If not there are several very very reputable Quadrajet rebuilders who specialize in Oldsmobiles..I am not close enough to you or I would come over and do it.... I taught myself over the years.,......

Bob

 

Not at all. I could take the air horn off, look down inside of it and recognize most of what's there but not know what is or isn't supposed to be there.